This invention pertains generally to microwave feed networks, and more particularly to microwave feed networks using waveguides to distribute radio frequency energy to elements of an antenna array.
A corporate feed network for an antenna array typically uses waveguides and waveguide junctions to distribute radio frequency (R.F.) energy to elements of the antenna array. A T-junction having two collinear ports and an orthogonal port may be used as a simple coupler by means of an aperture at the junction. The aperture couples a portion of the radio frequency (R.F.) energy from either of the collinear ports into the orthogonal port. Similarly, R.F. energy incident into the orthogonal port couples an equal amount of R.F. energy into the collinear ports.
Four-port junctions can be composed of two similarly shaped waveguides placed side by side, with an aperture providing the required coupling between them. When two or more appropriately spaced apertures are used between two parallel waveguides, power coupled into the secondary waveguide will propagate in only one direction, thus creating a directional coupler. Such a directional coupler is commonly called a three-decibel directional coupler, or a quadrature hybrid junction, dividing R.F. energy introduced at one port equally between two other ports and suppling little or no energy to the remaining port.
Using known coupling techniques, it is often necessary for a corporate feed network to be designed with complex twist sections and multiple bends to feed the elements of the antenna array correctly. Further, required spacing between the elements of an antenna array is often difficult to attain using known corporate feed networks. Typical four port couplers, because of their size and package form factor, may be unsuited. Three port couplers, while simplifying the complexity of a corporate feed network, compromise the performance of such a feed network. It is therefore desirable to create a coupler which, when used in combination, provides effective electrical performance, has mechanical simplicity, ease of construction, and optimum form factor packaging.